The great increase in energy prices which arose on the basis of political developments in recent years makes it imperative that a search be mounted for new sources of energy which up till now have been exploited either not at all or insufficiently.
In this regard the exploitation of deposits located at sea, whose exploitation could not be justified economically in earlier times, steps to the foreground. Thus even at the present time enormous quantities of gases admixed with oil are burnt off at the various sea wells and are thus lost to any economic use.
The employment of floating installations for purification, liquefaction, and intermediate storage for subsequent shipment in tankers is necessary for many of these deposits. The use of such floating units must also be considered for deposits which are not located at sea but rather in structurally underdeveloped or climatically unfavorable areas, since the construction of such technically complex systems in these countries themselves--the Near East--leads to very high costs and long construction times. Therefore it is advantageous, and this is particularly true for many discoveries at sea which are not of lasting productivity, that a floating system can be moved after the exhaustion of a discovery from there to another site.
Floating installations in which the liquefaction unit and the tank space are combined in one unit are already known. A Norwegian shipyard which builds LNG/LPG tankers, for example, has publicized a project in which three parts, whose construction roughly corresponds to sections of the middle of a LNG tanker, are combined in one unit. This is done in such a way that two sections, which contain the tank space, are placed together with their long axes parallel to each other while a third section, which supports the actual machine installation, is arranged transverse to these at one end and is firmly assembled to the other two.
Another known project provides for the use of a large pontoon with tanks arranged underneath which at the same time serve as pontoons. These tanks are shaped basically like large cylinders which taper conically at the upper end. Because of the low density of the liquified gases the tanks are very light, even when they are completely filled with LNG/LPG products.
The floating installations described up till now have certain disadvantages, partially from the practical/nautical viewpoint or, if one should disregard this, for economic reasons arising from the high costs of construction. In reference to the first project mentioned above, the anchoring of large gas tankers along the long side of floating installations whose draught is hardly greater than that of a gas tanker in order to transfer oil becomes almost impossible with even slight wind and wave levels. When a storm arises during the loading the process must be broken off so as to not endanger the ship and the liquefaction installation.
For this reason another project has been described. Here the gas tankers are not anchored along the long side but rather float free of the floating liquefaction installation and are connected with it merely by means of a long bow line and are then loaded over the bow by means of special hose lines which float or hang in a long loading boom. In this project the liquefaction installation is built on deep pontoons as a so-called "half-diver." The tank space for the liquefied gas, whose volume should be somewhat larger than that of the gas tanker which is to be loaded, is placed in the pontoons or on a special floating unit, fully separated from the liquefaction installation. Because of the low density of the liquid gases, very expensive constructions are necessary to keep the empty or filled tank spaces at a somewhat constant depth and to achieve sufficient stability.
The task of developing a floating gas liquefaction installation, including tank space, which in spite of lowered production expenditures in comparison with the above-described arrangements is characterized by improved stability in all loading conditions and to a great extent avoids the above-mentioned disadvantages underlies the invention.